Explain Capillary waves

Let us learn what is capillary waves,
A wave occurring at the interface between two fluids, such as the interface between air and water on oceans and lakes, in which the principal restoring force is controlled by surface tension.
A water wave of less than 1.7 centimeters. Also known as capillary ripple.

Surfaces of liquids are decorated with thermally activated capillary waves. Their amplitudes are on the order of angstroms. Many X-ray scattering experiments, which show the unambiguous fingerprints of capillary waves on liquid surfaces, have been performed in the past. These experiments, however, have tested the static time-averaged structure rather than the dynamics of the surface fluctuations. This is due to the major drawback that conventional X-ray sources are essentially incoherent, which renders the direct measurement of dynamics impossible. With high-brilliance third-generation sources it has become possible to obtain intense X-ray beams possessing a high degree of coherence. Such beams are produced by selecting the coherent part of the impinging radiation from an otherwise incoherent beam using micrometre-sized pinholes. These coherent beams make photon correlation spectroscopy with X-rays (XPCS) possible.
Hope the above explanation helped you.